Re: [Xen-devel] how to trace scheduling overheads using xentrace/xenalyze

["Yu-An(Victor) Chen" <chen116@xxxxxxx>]

Hi Dario,

Thank you very much for your reply!!! It is very nice of you :)

Yes I have checked the blog entry and that is actually where I started!

To define my "scheduling overhead", I think I should tell you what I am trying to accomplish:

So I am currently using Xen 4.5 to help us understand more about real time virtualization. When I am experimenting with Xen-4.5, I observed that the guest VM tend to perform not as well when there are a lot of small jobs in a given period.Â

I think the reason behind it is because even though the jobs are small, but there are so many tasks so the large amount of scheduling overhead for each job cause the performance to get worse.

So I want to measure the scheduling overhead for the tasks.

So I guess my definition for "scheduling overhead" in this case will be the time interval between when theÂclock interrupts for scheduling before a job is run and when the job starts.Â

Basically, I want to see how long does it take toÂscheduleÂa job and how long does it take to actually run the job.Â

So in that case just looking at howÂvcpus are scheduled is not enough?ÂIf you think this concept is incorrect, please correct me, thx!

Oh and yes I can get a similar output file by usingÂxentrace -D -e 0x0002f000 trace.bin &Âxenalyze dump-all.

that brings me to 2 more questions about how to read this dump-all output:

First Question: Âhow do I read those lines, for example :

Â0.000019969 x----------Â -- d32767v0Â Â22805(2:2:805) 5 [ 7fff 0 0 0 0 ]

I can only tell that the first number(Â0.000019969)Âmeans time, and d32767v0 means "domain 32767 at vcpu0".

what doesÂÂ22805(2:2:805) 5 [ 7fff 0 0 0 0 ] each stands for? hopefully it contain the information I need.

Second Question: Why are there domain 32768 and 32767? I never created those domains and they took up most of the dump-all file.

Again thank you very much for your reply. and sorry Âfor the long replies if my reply format is wrong, I am new to mailing list too.

Victor

On Wed, Oct 7, 2015 at 3:32 AM, Dario Faggioli <raistlin@xxxxxxxx> wrote:

On Tue, 2015-10-06 at 20:46 -0700, Yu-An(Victor) Chen wrote:
> Hi,
>
Hi,

> I am new to xen environment
>
Welcome :-)

> and I am wondering how to trace scheduling overhead of guest vm using
> xentrace/xenalyze ?
>
Have you had a look at this blog entry? It's from some time ago, but
the basic concepts should still hold.

Âhttps://blog.xenproject.org/2012/09/27/tracing-with-xentrace-and-xenal
yze/

Of course, that tells how to use the tools (xentrace and xenalyze), not
how to "trace scheduling overhead". For doing so, I think you should
first define what it is really that you want to measure (many
definitions of scheduling overhead are possible) and, only after that,
check whether it is possible to do that with existing tools.

> I have tried using $xentrace -D -e all -S 256 {filename}
>
> and then use various xenalyze options but most of them gave me empty
> result, and I dont really see where I can get scheduling overhead so

>
Mmm... The command above works for me (just tried). However, '-e all'
is a lot of data, and it may actually take a bit to xenalyze to parse
it.

Maybe, if you are interested in tracing scheduling related events, use
the appropriate event mask?

> I can see how are the jobs are scheduled and its execution time and
> stuff. Please point me to a direction. Thank you!
>
Again, you should detail more what you think 'scheduling overhead' is.
If you are interested in seeing how and where the vcpus are scheduled,
you want a dump.

With this:

Âxentrace -D -e 0x0002f000 trace.bin

and then this:

Âxenalyze --dump-all trace.bin

Here's an excerpt of what I get:

]Â 0.000019647 x----------Â -- d32767v0Â Â22802(2:2:802) 0 [ ]
]Â 0.000019969 x----------Â -- d32767v0Â Â22805(2:2:805) 5 [ 7fff 0 0 0 0 ]
 Â0.000020474 x---------- -- d32767v0 runstate_continue d32767v0 running->running
]Â 0.000021170 ----x------Â -- d32767v4Â Â22802(2:2:802) 0 [ ]
]Â 0.000021370 ----x------Â -- d32767v4Â Â22805(2:2:805) 5 [ 47fff 0 0 0 0 ]
 Â0.000021817 ----x------ -- d32767v4 runstate_continue d32767v4 running->running
]Â 0.000022235 ---------x-Â -- d32767v9Â Â22802(2:2:802) 0 [ ]
]Â 0.000022467 ---------x-Â -- d32767v9Â Â22805(2:2:805) 5 [ 97fff 0 0 0 0 ]
 Â0.000022983 ---------x- -- d32767v9 runstate_continue d32767v9 running->running
]Â 0.000023438 --------x--Â -- d32767v8Â Â22802(2:2:802) 0 [ ]
]Â 0.000023638 --------x--Â -- d32767v8Â Â22805(2:2:805) 5 [ 87fff 0 0 0 0 ]

Regards,
Dario
--
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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